The Massai calf, born on Feb. 25, underwent arthroscopic surgery this week to remove infected bone from his right shoulder, said zoo director Rick Barongi.

A week after Yao's birth, keepers noticed that he was favoring his rear left leg. Yao and his mother, Neema, were kept in a separate stall so officials could monitor what appeared to be a minor sprain that would improve with rest.

"We thought it was just something minor, that maybe it was too much exercise," Barongi said.

When the limp gradually became worse, however, zoo veterinarians X-rayed the leg and found no evidence of bone damage, officials said. The calf was put on antibiotics and other medication, including anti-inflammatory analgesics.

Winchell determined that Yao had developed a bone infection in his right shoulder and began an aggressive treatment regimen that included flushing the joint, removing the damaged tissue and infected bone, and administering stronger antibiotics.

"He's got a long road ahead," Winchell said Friday, a day after the surgery. "Having the problem in two joints, and having this infection involving the bone, it's going to be an upward battle for him, and we have a long way to get him back and see him through, unfortunately."

Feisty fighter

After the operation, he said, Yao was putting weight on the legs, although not as much on the two injured ones.

If any animal has the will to survive, it has to be Yao, said Barongi.

"This guy's pretty tough, and he's been a fighter," he said. "I've seen a lot of giraffes, and sometimes they'll give up if something's too stressful. Yao is feisty, and he's trying. Even with his mom, when he wants to nurse he lets her know."